In order to ensure the performance and quality of their products, semiconductor memory device manufacturers perform a battery of tests on the devices. Among these tests are measurements of device performance parameters. One important device parameter is access speed.
Formerly, PROMs and EPROMs (electrically programmable read only memories) have been tested by actually programming the memory cells, testing the devices, and then erasing the devices by exposure to ultraviolet light for a period of time. To permit the penetration of ultraviolet light, the devices are contained in expensive packaging with light transmitting windows. Although this test method has been somewhat satisfactory, the expense of providing the transparent window packaging has prompted development of alternate test methods.
An apparatus and method to improve the testability of one-time programmable memory devices are described in U.S. Pat. No. 4,740,925, issued to Kaszubinski et al. on Apr. 26, 1988, and assigned to Texas Instruments. Kaszubinski et al. provide an extra row of memory cells which are programmed during testing. Speed measurement is performed by alternately reading memory cells in an extra programmed row and memory cells in the rest of the rows in the device.
However, in a memory device which has segmented memory cell arrays, an extra row of memory cells and its associated decoding circuitry are required for each segment of the arrays. A method is herein provided that does not require the extra row of memory cells and associated circuitry to perform the speed measurement test.
The present invention provides for a method for measuring the speed of PROMs and is directed to overcoming the problems as set forth above.